In the Manual’s edition, we added two significant pieces of information to each alliance description: a species life history traits table and a fire regime table. The tables provide a better ecological characterization of the alliance. An alliance exists because the principal species is (are) adapted to certain environmental settings, and because related species that make up the alliance are able to coexist in a shared environment. Typically, ecologists explain the ecological constraints of a community of plants by finding correlations with environmental variables, such as temperature, precipitation, soil chemistry, and substrate texture. They also find strong temporal aspects and responses to disturbances that also drive species patterns. Ecologists recognize these variables widely as another important measure of understanding why vegetation patterns exist in certain predictable arrangements. Chief among these are various types of natural disturbance processes, such as fire, flood, disease, and long- and short-term climatic fluctuations. Fire is one of the best understood and most studied of these variables in California because of the interest it has generated over the years with its regular summertime impact on landscapes and human infrastructure in our dry Mediterranean climate.
In the species life history traits tables, we summarize the physiological constraints and adaptations of each characteristic species of the alliance. The tables underscore the relationship between the species and the vegetation type. They provide the basic information to allow us to address complex questions, such as “Why are stands of the Arctostaphylos viscida alliance found on the tops of the ridges, but not on lower slopes?” This pattern has to do with multiple factors, some hard (e.g., it is on the ridge in part because of the root structure and leaf morphology of the species, which can compete successfully in very rocky, well-drained substrates) and some soft (e.g., the time since the last fire or other disturbance, and the disturbance’s intensity and periodicity).
In the fire regime tables, we summarize the interval, intensity, size, and complexity of fires experienced by stands of the alliance, whether natural or human-mediated. These are highly characteristic and reliable explanatory variables. For example, stands of annual grassland always burn at a much higher frequency, though much lower intensity, than adjacent stands of coast live oak woodland. The dominant species set up (and are set up by) the alliance’s propensity for fire, its regularity, and its intensity. We provide fire tables only for those alliances where research and expert information clearly show fire as a strong influence and driving factor.
To further explain and summarize the tables, we provide two appendixes that denote the terms, definitions, and codes used in the two tables. In these appendixes, we also provide comprehensive tables for the species life history traits and alliance fire regime information.
The professional community of fire ecologists and managers in California has provided strong support for these additions in the new edition. Concurrent with its development, the Association of Fire Ecologists (AFE) produced a broad-spectrum book on California’s fire ecology (Sugihara et al. 2006). Our two organizations have had much interaction, especially during earlier stages, to standardize the terms used in the AFE book and in this edition. Both books act as catalysts for refining our understanding of how best to manage the wildlands of the state.